In mammals, glucuronidation is a principle means of detoxifying or inactivating compounds which utilizes the UDP glucuronyl transferase system. In humans, a number of hormones, including cortisol and aldosterone testosterone and androsteindione, certain antibiotics such as chloramphenicol, toxins such as dinitrophenol, and bilirubin are among the compounds which are conjugated to form glucuronides by the glucuronyl transferase system and then excreted in urine or into the lower intestine in bile. The bacterium Escherichia coli has evolved to survive in the mammalian intestine, and can utilize the excreted .beta.-glucuronides as its sole carbon source. To do so, E. coli has evolved mechanisms for the uptake and degradation of a wide variety of glucuronides, processes which are tightly linked genetically.